The present invention relates to a method for detecting knock generated in an internal combustion engine such as an automotive engine, and more particularly, to a method for controlling timing and period for detecting the knock.
A learning control system for correcting ignition timing has been proposed. The control system is adapted to advance the ignition timing so as to produce a maximum torque as long as the level of the engine knock does not exceed a tolerable level. If the knock occurs, the control system operates to retard the ignition timing by a predetermined value.
The knock, which occurs during a combustion stroke in a cylinder after ignition, is detected by sensing vibrations of the engine by a knock sensor. However, there are the vibrations generated from sources other than the knock such as a valve seat which generates the vibration when the valve strikes the valve seat. Therefore, the knock must be detected in a period of time between certain crank angles, for example between 30 and 90 degrees after top dead center (ATDC), when the valves do not operate. The knock detecting period is controlled in accordance with engine operating conditions.
Japanese Patent Application Laid-Open 56-2469 discloses a control system of a knock detecting period where a gate signal is provided for taking out a knock signal from various signals. A period generating a gate signal is controlled in accordance with engine speed.
However, since the knock detecting period is determined only in dependency on the engine speed, the system cannot cope with a situation where the ignition timing greatly changes. More particularly, in a learning control system of ignition timing for an engine provided with a supercharger, the ignition timing is controlled in accordance with the engine speed and other conditions such as a change of a octane number of fuel supplied thereto, so that the ignition timing is greatly advanced or retarded. The knock generating timing greatly changes with the ignition timing. Thus, it is difficult to accurately detect the knock in any engine operating condition.